1. Field of the Invention
The present invention relates to an apparatus for detecting abnormal states of an optical disc recording/reproducing apparatus, and more particularly, to an apparatus for detecting abnormal states, which can swiftly prevent damage to a laser diode and data recorded on a disc.
2. Description of the Related Art
An optical disc recording/reproducing apparatus is an apparatus which applies laser light generated in a laser diode to a recording area so that data is recorded or reproduced. During recording and/or reproduction, the laser light generated in the laser diode should maintain an appropriate output with respect to operation modes.
An apparatus for controlling a laser diode output must accurately maintain the output of the laser diode in response to the operation modes of the laser diode, and changes in input and output characteristics. The apparatus detects the output of the laser diode by a monitor diode, and controls the output of the laser diode by comparing the detected output with a desired value.
If overflow or underflow occurs in the output of the laser diode, the laser diode may be damaged or data may be incorrectly recorded or lost. Therefore, to prevent the overflow condition or the underflow condition, a circuit for detecting abnormal states is provided.
FIG. 1 is a block diagram of a prior art apparatus for detecting abnormal states.
The apparatus of FIG. 1 includes a first comparator 112 which detects overflow, a second comparator 114 which detects underflow, and a microprocessor 120 which provides overflow and underflow setting values to the first and second comparators 112 and 114, respectively.
A monitor PD & current/voltage (I/V) converter 102 detects an output level of a laser diode 110. The output level detected by the monitor PD & current/voltage converter 102 is amplified in a variable gain amplifier 104. The amplification degree of the variable gain amplifier 104 changes depending on the operation modes (reproducing/recording) of the optical recording/reproducing apparatus and whether the recording/reproduction apparatus is currently accessing tracks/grooves.
The output of the variable gain amplifier 104 is provided to an APC block 106. The APC block 106 compares an input provided by the variable gain amplifier 104, that is, the current output of the laser diode, with a reference value, and controls the output of the laser diode 110 according to a result of the comparison.
The output of the APC block 106 is provided to the laser diode 110 through a Digital/Analog Converter (DAC) 108, to control the output of the laser diode 110.
In the apparatus shown in FIG. 1, if the output of the laser diode 100 is too high (overflow), the laser diode 110 may be damaged and data recorded on the disc (not shown) during recording may be damaged; and in reproducing, recorded data may deteriorate to affect recording quality or recorded data may be damaged to be unreproducible.
Meanwhile, if the output of the laser diode 110 is too low (underflow), a normal reproducing signal from a pick-up (not shown) is not obtained, and the APC block 106 does not sense the output level of the laser diode 110, so the output level is not controlled.
To prevent deteriorating recording quality and damaging recorded data, a circuit for detecting abnormal states detects a state in which the output of the laser diode 110 is too high (overflow) or too low (underflow), so that appropriate measures are taken.
In the apparatus of FIG. 1, the first comparator 112 detects overflow by comparing the output of the variable gain amplifier 104, that is, the current output level of the laser diode 110, with an overflow setting value, and generates a signal which indicates an occurrence of overflow according to a result of the comparison.
Meanwhile, the second comparator 114 detects underflow by comparing the output of the variable gain amplifier 104, that is, the current output level of the laser diode 110, with an underflow setting value, and generates a signal which indicates an occurrence of underflow according to a result of the comparison.
The microprocessor 120 monitors the states of the overflow signal generated in the first comparator 112 and the underflow signal generated in the second comparator 114, recognizes whether an abnormal state occurs, and if an abnormal state occurs, takes appropriate measures.
However, because the microprocessor 120 monitors whether overflow and underflow occur and performs operations for coping with abnormal states, the prior art apparatus for detecting abnormal states of FIG. 1 does not avoid delays due to processing by the microprocessor. That is, the microprocessor recognizes the occurrence of overflow and underflow by an interrupt signal, and spends times processing the interrupt. Therefore, due to the delay time for processing the interrupt, the microprocessor does not swiftly take measures to protect the laser diode or data recorded on the disc. In addition, in an optical disc recording/reproducing apparatus having a large capacity or high speed, data recorded on a disc or a laser diode in the apparatus is more vulnerable to damage due to the delay time.